Establishing the authenticity of food products, and in particular, extra virgin olive oil (EVOO) continues to be of great interest to scientists and consumers, and detecting adulteration of EVOO for economic gain is an ongoing concern for regulatory agencies. Adulteration of EVOO, involving the replacement of high cost EVOO with lower grade and cheaper substitute oils can be very attractive and lucrative for a food manufacturer or raw material supplier. The adulteration of EVOO can also have major health implications to consumers. As such, the detection of EVOO adulteration is of importance.
There are many olive oil standards that have been approved and published by various associations and countries, which standards define grades of olive oils and specify chemical composition and quality parameters. These standards are regularly amended to accommodate the natural variations in olive oil cultivars and to upgrade them if new components are discovered in EVOO. These standards also typically include various recommended analytical techniques that can be used to verify the grade and quality of the oil being tested. In fact, a variety of prior art physical and chemical tests have been used to establish the authenticity of olive oil and to detect the level of adulterants in it.
Suggested techniques include the analysis of fatty acid profile of an oil, after methylation using gas chromatography (GC). High Performance Liquid Chromatography (HPLC) analysis of the fatty acid and triglycerides composition has also been studied. Further, approaches based on Nuclear Magnetic Resonance (NMR) analysis, or spectroflourometric methods have also been reported for detecting the adulteration of olive oil. However, many of these suggested methods used to detect adulteration of EVOO are labour intensive and/or are time consuming.
It should also be noted that previously, the desired development of a reliable and rapid method to detect adulteration of EVOO was found to be challenging and generally considered to be extremely difficult using a single analysis. Chemical methods combined with chromatographic separations of fatty acid methyl esters (FAME) or triacylglycerol (TAG) are only effective to detect the presence of added edible oils to EVOO products provided the composition of the adulterated oil mixture is sufficiently different from that of EVOO, i.e., contain higher FA levels of 18:2n-6, 18:3n-3, and 16:0, lower levels of 18:1n-9 and 16:0, or possess a different TAG structure compared to that of EVOO. In such cases, it might be possible to detect a 10 or 20% addition, but this approach has limited utility. For example, one could not detect the addition of a fully refined olive oil to an EVOO since both oils would have the same FA and TAG compositions.
UV spectroscopy based on 208-210 and 310-320 nm has also been widely used to detect the adulteration of extra virgin olive oil with refined olive oil. Unlike chromatographic procedures, vibrational spectroscopy techniques offers unique advantages because they are typically rapid, non-destructive, and can be applied to measure neat oils without any sample preparation or dilution in any solvent.
Similarly, mid-infrared (MIR) and near-infrared (NIR) spectroscopic techniques in conjunction with multivariate statistical methods have also been used to analyse and classify EVOO.
In our previous document, namely PCT Patent Application No. PCT/CA2016/000026, the contents of which are incorporated herewith in their entirety, we described an analytical technique for the detection of EVOO adulteration based on an FT-NIR analysis approach. In this approach, an FT-NIR calibration matrix (or model) was prepared based on analysis of known EVOO samples. The calibration matrix analysis included results from authentic EVOO samples, or EVOO samples spiked with various edible oils as adulterants, and additionally based on the results of a comparison of EVOO samples analysed by FT-NIR and also analysed by prior art analytical techniques (such as the results from GC analysis).
In this approach, the FT-NIR analysis can be used as a rapid method for the authentication of the various constituents of an EVOO sample. This includes the identification of the various constituent oils in the sample, and their respective concentrations.
Moreover, the purity of the oil sample, can be determined based on the spectral analysis of the sample oil at a specific frequency range, when compared to the value at this specific frequency range for an authentic oil. It was determined in PCT application No. PCT/CA2016/000026, that using an FT-NIR analysis conducted at a wave number centered at, or centered essentially at, around 5280 cm−1, was preferred.
By using the phrase “essentially at”, the skilled artisan will be aware that the band found at or near 5280 cm−1, is to be analysed, and compared to a known EVOO spectrum. In actual fact, the levels found for this band can be analysed over a wave number range of about 5280+/−50 wave numbers. In any event, while there is some latitude in the exact wave number used, it was clear that the FT-NIR spectroscopy analysis peak centered at approximately 5280 cm−1 is a FT-NIR spectroscopy peak which is of interest in determining the authenticity of an oil sample.
Further, in PCT/CA2016/000026, it was described that the results obtained in the region of essentially 5280 wave numbers, could be compared to the FT-NIR results obtained for the known sample, centered at a wave number of essentially 5180 wave numbers. Again, the term “essentially”, is to be interpreted as the results obtained over a wave number range of about 5180+/−50 wave numbers. Comparison of the ratio of these two wave number results, at both 5180 and 5280 wave numbers, in an authentic EVOO sample, and the ratio of these two wave number results in an unknown sample, allowed the development of an “FT-NIR Index” value. This value is the area under the curve at essentially 5280 wave numbers, divided by the area under the curve at 5180 wave number, and normalized to a value of 100. As such, for an authentic EVOO sample, the FT-NIR Index value should be at or about 100 since the ratios of the two wave number results obtained for the sample and for the authentic EVOO standard, should be the same. Variations from this value indicate an increasing possibility of adulteration, or degradation of the olive oil being tested. Consequently, the FT-NIR Index is at its highest (e.g. typically 100) when authentic EVOO is tested. In actual testing, indices of over 80 are preferred, with levels of over 90, 95 or even more 99, being even more preferred. Once the index falls below these levels (and particularly below the lower levels), adulteration or degradation of the oil sample is to be suspected.
As a result, the previous approach provided a single screening method that would rapidly authenticate a wide variety of EVOO samples, determine the constituent elements of an oil sample, and, if present, identify the nature (identity) and concentration of an adulterant in the EVOO sample.
However, while the previous technique provided a valuable tool for the rapid analysis of a number of different EVOO samples, it has been noted that analysis of some samples could be enhanced to provide a better indicator of whether the sample has been adulterated or the like.
As such, providing an improved, and more robust, rapid analysis method for the authentication of the constituents of an EVOO sample would clearly be beneficial. This would be particularly advantageous if the analytical technique could be used to rapidly verify the authenticity of a wider range of EVOO samples in order to verify that they were essentially authentic EVOO.
As such, it would be advantageous to be able to provide an improved and more robust, rapid technique for determining whether an edible oil sample, and in particular an EVOO sample, had been adulterated, and if so, identify the type, nature, and/or amount of EVOO adulteration that had occurred.